Variable pitch propeller



I Sept 10, 1946- K. B. GILLMORE ETAL l l.2,407,414

'VARIABLE PITCH PROPI'LLER vFiled July 7, 1942 sa al 3' 27 /oA 2^ y 'o l2 kl l M 3o: ii' 3/ 27 29 25" 29 225@ f4: bis f4; ,8 /7 /7 l5 l/l 1 /l 1 q 3 :NVE/vrom KENNETH B. GILLMQRE BY Groks: HE BRowN Patented Sept. 10, `1946 VARIABLE PITCH PROPELLER Kenneth Bryan Gillmore and George Henry Fitzroy Brown, Hatfield, England, assignors to The De Havilland Aircraft Company Limited, Hatfield, England Application July 7, 1942, Serial No. 450,031 In Great Britain April 15, 1941 2 claims. (o1. 17o-135.6)

The present invention consists in a variable pitch airscrew pitch control mechanism comprising a gear train for operative connection between the airscrew blades and a Apitch-change drive input gear, said gear :train being constituted by two sun gears mounted coaxially of the airscrew shaft, and reversing gearing operating between the two sun gears and carried by a rotatable cage mounted coaxially of the airscrew shaft; one of the sun gears also operatively engaging the pitchchange drive input gear, whereas the other meshes also with a pitch-change drive output gear operatively connected to the airscrew blades.

Such pitch-change mechanism presents the advantage that it is capable of such standardisation that it may be installed either as pitchchange transmission gearing in a single airscrew, or as duplicator means between the front and rear airscrews of a counter-rotating airscrew assembly; or between any two ror more alternately oppositely rotatable airscrews disposed in tandem.

The arrangement further provides duplicator mechanism in simple form for interposition'be-` tween two airscrews disposed in tandem, or between the front and rear airscrews of a counterrotating airscrew assembly, such as will in operation ensure precisely equal and opposite pitchchange in both interrelated airscrews.

In order that it may be clearly understood and readily carried into effect, the invention is hereinafter described with reference to the accompanying diagrammatic drawing, of which:

Figure l indicates very diagrammatically airscrew pitch control mechanism according to the invention applied to a single airscrew;

Figure 2 is an isometric view illustrating the nature of the reversing gearing included in the planet trains; while Figure 3 is, again, a very diagrammatic illustration of the invention as applied ,for pitchohange control of both airscrews of a counterrotating airscrew assembly.

Referring first to Figures 1 and 2, the su-n wheel I is fixed on the airscrew shaft I I and thus rotates with it; whereas the sun Wheel I 2 is fixed against rotation under restraint of the means connecting it, for example to the engine, indicated at I3. A planet-carrying cage I4 is mounted for rotation as a whole about the airscrew shaft I I and mounts two sets of planets or reversing gearing.

'I'he first set of planet or reversing gearing is constituted by the reversing pinions I5 and I6,V

of which the pinion I5 is rotatable about the axis of the shaft I1 carried by the cage I4, while the f pinion I 6 is rotatable about the shaft I8, also carried by the cage I4. The pinionsk l5 and Iii intermesh; the pinion I5 also meshes with the sun wheel I0; whereas the pinion I6 meshes with the sun wheel I2. It thus follows that, since in the arrangement shown in Figure 1 the gearing may be presumed to be symmetrical about the reversing pinions I5 and I6, the cage I4 rotates as a whole about the airscrew shaft at half the speed of the airscrew shaft II and in the same direction as the shaft.

The second set of planet gearing is constituted by the planet I9 fixed on the shaft 20 carried by the cage, which shaft'20 also mounts the revfersing pinion 2I. The reversing pinion 2| meshes with the cooperating reversing pinion 22 fixed on the shaft 23 carried by the cage, upon which shaft is mounted the planet 24. The planet I9 meshes with the annulus 25 of the sun wheel 28; whereas an annulus 21, similar to 25, meshes with the pitch-change drive input gear 28. Likewise, the planet 24 meshes with the annulus 29 of the sun Wheel 30, which also has the annulus 3 I meshing with a pitch-change drive output gear 32 on the shaft 33. The shaft 33 mounts the worm 34, which engages the worm wheel 35 directly connected to the shank of the airscrew blade, represented at 36, which is rotatable about the spider arm 31 fixed on the airscrew shaft I I.

The pitch-change drive input gear 28 is fixed on the pitch-change drive shaft 38 rotatable by any convenient means, such as a manually-operable device, `an electric motor, or an hydraulic motor; or the shaft 38 may be engine-driven with provision for drive reversal.

Figure 2 in its isometric form shows the reversing pinions 2| and 22 intermeshing for' drive reversal through the planet train; and it will be realised that the reversing pinions I5 and I6 opcrate in the same way between the sun wheels I0 and I2. In practice, the shafts I1, I 8, 20 and 23 will extend right across the cage I4, but for purposes of diagrammatic representation those shafts have been shown extending from one side of the cage to the adjacent side of the nearest reversing pinion.

The operation of the transmission gear shown and described with reference to Figures 1 and 2 is as follows: Rotation of the airscrew shaft II, taking with it the sun4 wheel I0the spider arm 31, together wtih the blade shank represented at 3S, drives the reversing pinion I5. The reversing pinion in its turn meshes with the reversing pinion I6, but thepinion- I6 cannot rotate freely because it meshes with the stationary sun wheel.

I2. As stated, therefore, the cage rotates in the same direction as the airscrew shaft II at half the speed thereof. The spider arm 31 can be regarded as a member integral with the airscrew shaft II, so that the airscrew hub is also rotating with the airscrew shaft; `and so long as n pitch-change operation is in progress, the pitchchange drive output gear 32 must not rotate about the axis of its shaft 33. Therefore, the gear 32 and the sun annulus 3l rotate about the axis of the shaft II as though they were interlocked, and the sun annulus 29 therefore also rotates at the same speed as the airscrew hub, transmitting drive through the planet 24, reversing pinions 22 and 2l, so that the planet I9' rotates on the shaft in the opposite direction to that of the planet 2li about the shaft 23. The transmission therefore resolves itself into a system whereby, although the sun annulus 25 is in a sense rotating oppositely with respect to the airscrew hub, it is in fact stationary with respect to the engine or some other stationary part, as indicated at I3.

For pitch-change operation, the shaft 33 is driven in the required sense, with the result that the pitch-change input gear 28 rotates in the same sense; and, by virtue of its engagement with the sun annulus 21, either adds to or subtracts from the normal speed of rotation of the gear I9.

At this stage it is well' to emphasize again the diagrammatic nature of the drawing, for to deal with loads likely to be encountered in pitchchange operation reduction gearing may have to be introduced as between the pitch-change transmission mechanism and the pitch-change drive.

Referring now to the arrangement shown in Figure 3, wherein the pitch-change mechanism is applied to a counter-rotating airscrew assembly, the pitch-change transmission mechanism operating between the pitch-change drive input gear and the rear airscrew is the same as that shown and described with reference to Figures 1 and 2. The required duplication and reverse rotation as between the two airscrews, however, involve the duplication of the pitch-change mechanism. Thus, the pitch-change which is made by the mechanism described and illustrated with reference to Figure 1 is transmitted forwardly past the rear airscrew 35, so that the gear 23', under the influence of the pitch-change drive input gear`28` of the rear airscrew, rotates in the same sense and direction as the opinion 32, and thus becomes the pitch-chang-e drive input gear for the more forward airscrew, as represented by the blade shank 36. The arrangement of the reversing pinions I5', I6' and shafts I'I, I3 in the cage I4' is the same as that of the parts I5, IS, I'I and I8 of Figure 1; but, be it noted, the reversing pinion I5 meshes with the sun annulus ISA on the forward airscrew shaft IIA; whereas the reversing pinion I6' meshes with both the reversing pinion I5' and the sun gear IZA fixed on the rear airscrew shaft II, which is tubular to accommodate the airscrew shaft I IA; and in consequence it follows that the cage I4', assuming symmetry of the gearing, will rotate at the mean speed of the two airscrews, thus assuming symmetry of the duplicator gearing about the reversing pinions 2|', 22'; and also assuming that the airscrew shafts II and IIA are rotating at the same speed but in opposite senses, then the cage I4' will remain stationary. Again, as with the arrangement described with reference to Figure 1, pitch-change will occur if the more forward airscrew pitch-change drive output gear 32' is caused to rotate about the axis of its shaft 33';

and it therefore follows that so long as no pitchchange operation is in progress the gear 32' has to rotate interlocked with the sun annulus 3l' about the axis of the airscrew shaft IIA The sun annulus 29' rotates similarly to effect rotation of the planet 24 about its shaft 23. Rotation of the shaft 23' is reversed through the reversing pinions 22' and 2 I shaft 20', with the result that the sun annulus 25' rotates in a sense which, though reverse to the sense of rotation of the sun annuli 22', SI', in fact results in the annulus 25 remaining stationary about the axis of the outer airscrew shaft II. The additive or subtractive effect caused by rotation of the forward airscrew pitch-change drive input gear 23 about its axis causes a change in the rotation of the gear IQ', in accordance with the sense of rotation, with consequent transmission of pitchchange drive. Symmetry of the gear about the reversing pinion ensures precisely equal and opposite pitch-change as between the blade shanks 36 and 36.

it is to be understood that the transmission mechanism by which the pitch-change operation is transmitted to the rear airscrew assembly, indicated by the blade shank 36 in Figure 3, may be of any convenient type. Figure 3, however, serves to show an` arrangement in which the transmission is virtually duplicated in a counterrotating airscrew so as to serve, not only for transmission of pitch-change drive to the rear airscrew assembly, but also as duplicator mechanism for operation between the rear and forward airscrews of a counter-rotating airscrew assembly so as to ensure precise equality of pitchchange but in opposite senses.

As above stated, equality of pitch-change results from the symmetry of the gear about the axis of the pitch-change reversing pinions 2l', 22'; and if a situation should arise wherein a predetermined inequality of pitch-change is required as between the front and rear airscrew of a counter-rotating airscrew assembly, it can be provided by deliberately designing the pitchchange gearing of the duplicator asymmetrically about the reversing pinions 2 I 22',

The function of the reversing pinions I5, Iii, I5', IS' is not immediately apparent, and it is therefore desirable to explain that they operate to control rotation of the cage I4 or It', as the case may be. if the reversing pinions i5, I6, I5', I6' were not provided there would be nothing to take the reaction of pitch-change transmission loads and in that event driving of the pitch-change input gear would, against any appreciable blade loads, merely result in movement of the cage.

What we claim is:

1. Control mechanism for variable pitch airscrews, comprising a pitch-change input drive gear, a cage mounted coaxially of and for rotation relative to the airscrew shaft, pitch-change control gearing and pitch-change reaction gearing; each such set of gearing including two spaced shafts journaled within said cage and a gear on each shaft intermeshing to reverse the relative sense of rotation of the two shafts, the reversing gears of one set being split to locate one half axially distant from the companion intermeshing half on each shaft thereof, the pitchchange reaction gearing further including a sun gear within the cage rotatable with the airscrew shaft and. meshed with one of its reversing gears, and a second sun gear within the cage secured to a static anchorage and meshed with the second of its reversing gears; the pitch-change control gearing further including a split sun gear, one half being external of the ycage and operatively connected to the pitch-change input drive gear and the other half being internal of the cage and meshed with the distant half of one of the split reversing gears, and also including a second split sun gear, of which one half is internal of the cage and meshes with the distant half of the second of the split reversing gears, and thev other half is external and operatively connected to the airscrew blades.

2. Control mechanism for a counter-rotating tandem variable pitch airscrew assembly which includes an inboard and an outboard airscrew, and a pitch-change input drive gear, such control mechanism comprising pitch-change control gearing and pitch-change reaction gearing for each such airscrew; each such set of gearing comprising two sun gears mounted coaxially of its respective airscrew shaft and reversing gearing operatively interposed between them; a cage mounted coaxially of and rotatable With respect to the airscrew shafts, supporting and enclosing both sets of reversing gearing; the sun gears of 6 the pitch-change control gearing for the inboard airscrew being operatively connected one to the pitch-change input drive gear and the other with .the blades of such inboard airscrew, and the sun gears of the pitch-change reaction gearing for the inboard airscrew being operatively connected one to the shaft of such inboard airscrew, and the other to a static anchorage; the sun gears of the respective sets of gearing for the outboard airscrew being similarly arranged and connected, except that the sun gear of the outboard airscrew which corresponds to the statically anchored sun gear of the inboard airserew is instead anchored to the shaft of the inboard airscreW, and in that the blade-connected sun gear of the pitch-change control gearing of the inboard airscrew is operatively connected to that sun gear in the outboard airscrew which corresponds to thel input drive gear-connected sun gear of the inboard airscrew; said pitch-change control mechanism for each airscrew being organized and arranged to produce pitch-change movements in opposite senses, but of unlike angular extent, as between thev blades of the two airscrews.

KENNETH BRYAN GILLMOREL GEORGE HENRY FITZROY BROWN. 

